NF-κB p50 facilitates neutrophil accumulation during LPS-induced pulmonary inflammation

BACKGROUND: Transcription factors have distinct functions in regulating immune responses. During Escherichia coli pneumonia, deficiency of NF-κB p50 increases gene expression and neutrophil recruitment, suggesting that p50 normally limits these innate immune responses. p50-deficient mice were used to determine how p50 regulates responses to a simpler, non-viable bacterial stimulus in the lungs, E. coli lipopolysaccharide (LPS). RESULTS: In contrast to previous results with living E. coli, neutrophil accumulation elicited by E. coli LPS in the lungs was decreased by p50 deficiency, to approximately 30% of wild type levels. Heat-killed E. coli induced neutrophil accumulation which was not decreased by p50 deficiency, demonstrating that bacterial growth and metabolism were not responsible for the different responses to bacteria and LPS. p50 deficiency increased the LPS-induced expression of κB-regulated genes essential to neutrophil recruitment, including KC, MIP-2, ICAM-1, and TNF-α suggesting that p50 normally limited this gene expression and that decreased neutrophil recruitment did not result from insufficient expression of these genes. Neutrophils were responsive to the chemokine KC in the peripheral blood of p50-deficient mice with or without LPS-induced pulmonary inflammation. Interleukin-6 (IL-6), previously demonstrated to decrease LPS-induced neutrophil recruitment in the lungs, was increased by p50 deficiency, but LPS-induced neutrophil recruitment was decreased by p50 deficiency even in IL-6 deficient mice. CONCLUSION: p50 makes essential contributions to neutrophil accumulation elicited by LPS in the lungs. This p50-dependent pathway for neutrophil accumulation can be overcome by bacterial products other than LPS and does not require IL-6

Nuclear Factor-B p50 Limits Inflammation and Prevents Lung Injury during Escherichia coli Pneumonia

Inflammatory responses to infection must be precisely regulated to facilitate microbial killing while limiting host tissue damage. Many inflammatory genes are regulated by B sites, and the p50 subunit of nuclear factor-B suppresses the expression of Bassociated genes in vitro. We hypothesized that p50 is essential to prevent excessive inflammation and injury during infection. During pulmonary infection with Escherichia coli, the gene-targeted deficiency of p50 did not affect bacterial clearance from mouse lungs, but it resulted in increased expression of proinflammatory cytokines 6 to 24 hours after infection. This dysregulation exacerbated inflammation (neutrophil recruitment), respiratory distress (pulmonary edema and blood gas exchange impairment), and decompartmentalization (transit of protein and bacteria from the air spaces to the blood). We interpret these studies to indicate that endogenous p50 protects the host by curbing inflammatory responses to prevent injury, essential to survive pneumonia

Proteins and Recruitment of Neutrophils during Escherichia coli Pneumonia

Interleukin (IL)–6 concentrations are positively associated with the severity of pneumonia, and this cytokine is essential to surviving experimental pneumococcal pneumonia. The role that IL-6 plays during pneumonia and its impact during gram-negative bacterial pneumonia remain to be determined. During Escherichia coli pneumonia, IL-6–deficient mice had increased bacterial burdens in their lungs, indicating compromised host defenses. Decreased neutrophil counts in alveolar air spaces, despite normal blood neutrophil counts and survival of emigrated neutrophils, suggested that defective neutrophil recruitment was responsible for exac-erbating the infection. Neutrophil recruitment requires nuclear factor (NF)–kB, but IL-6 was neither sufficient nor essential to induce NF-kB–mediated gene expression in the lungs. In contrast, IL-6 induced the phos-phorylation of signal transducer and activator of transcription (STAT) 1 and STAT3 in the lungs, and STAT1 and STAT3 phosphorylation during E. coli pneumonia was decreased by IL-6 deficiency. Thus, IL-6 plays essential roles in activating STAT transcription factors, enhancing neutrophil recruitment, and decreasing bacterial burdens during E. coli pneumonia. Lower respiratory tract infections are the leading cause of disability-adjusted life years lost worldwide [1] and are the leading cause of hospitalizations and deaths du

Roles for early response cytokines during Escherichia coli pneumonia revealed by mice with combined deficiencies of all signaling receptors for TNF and IL-1.

During infection, inflammation is essential for host defense, but it can injure tissues and compromise organ function. TNF-alpha and IL-1 (alpha and beta) are early response cytokines that facilitate inflammation. To determine the roles of these cytokines with overlapping functions, we generated mice deficient in all of the three receptors mediating their effects (TNFR1, TNFR2, and IL-1RI). During Escherichia coli pneumonia, receptor deficiency decreased neutrophil recruitment and edema accumulation to half of the levels observed in wild-type mice. Thus these receptors contributed to maximal responses, but substantial inflammation progressed independently of them. Receptor deficiency compromised antibacterial efficacy for some infectious doses. Decreased ventilation during E. coli pneumonia was not affected by receptor deficiency. However, the loss of lung compliance during pneumonia was substantially attenuated by receptor deficiency. Thus during E. coli pneumonia in mice, the lack of signaling from TNF-alpha and IL-1 decreases inflammation and preserves lung compliance